A SIMPLE 401k and a SIMPLE IRA are 2 distinctly different retirement plans with different contribution rules.
I would hesitate modifying your employer issued W-2.
Individual Retirement Arrangements (IRAs)Roth IRAs401(k) PlansSIMPLE 401(k) Plans403(b) PlansSIMPLE IRA Plans (Savings Incentive Match Plans for Employees)SEP Plans (Simplified Employee Pension)SARSEP Plans (Salary Reduction Simplified Employee Pension)Payroll Deduction IRAsProfit-Sharing PlansDefined Benefit PlansMoney Purchase PlansEmployee Stock Ownership Plans (ESOPs)Governmental Plans457 PlansMultiple Employer Plans
